How to Add a Memo to a Transaction

import {
  airdropFactory,
  appendTransactionMessageInstructions,
  createSolanaClient,
  createTransaction,
  generateKeyPairSigner,
  getSignatureFromTransaction,
  lamports,
  pipe,
  setTransactionMessageFeePayerSigner,
  setTransactionMessageLifetimeUsingBlockhash,
  signTransactionMessageWithSigners
} from "gill";
import { getAddMemoInstruction } from "gill/programs";

const { rpc, rpcSubscriptions, sendAndConfirmTransaction } = createSolanaClient(
  {
    urlOrMoniker: "localnet"
  }
);

const sender = await generateKeyPairSigner();
const LAMPORTS_PER_SOL = 1_000_000_000n;
await airdropFactory({ rpc, rpcSubscriptions })({
  recipientAddress: sender.address,
  lamports: lamports(LAMPORTS_PER_SOL), // 1 SOL
  commitment: "confirmed"
});

const memoInstruction = getAddMemoInstruction({
  memo: "Hello, world!"
});

const { value: latestBlockhash } = await rpc.getLatestBlockhash().send();
const tx = createTransaction({
  feePayer: sender,
  version: "legacy",
  instructions: [memoInstruction],
  latestBlockhash
});

const signedTransaction = await signTransactionMessageWithSigners(tx);

const transactionSignature = getSignatureFromTransaction(signedTransaction);
console.log("Transaction Signature:", transactionSignature);